Large amounts of palm oil are produced every year in oil palm growing countries, such as Malaysia and Indonesia. Palm fresh fruit bunches (FFB) are processed in palm oil mills to palm oil, multiple lignocellulosic coproducts and an aqueous effluent referred to as palm oil mill effluent (POME). About 2.5 tons of POME are produced per ton of oil. Part of the lignocellulosic material is burned for process energy, but most of it is not usefully applied. In some cases electricity is produced during this process, however, some of the lignocellulosic material is not used due to difficulties in burning it.
POME presents a major problematic environmental issue. It is hot (80-90° C.) and slightly acidic. Reported concentration ranges for oil/grease levels, BOD (biological oxygen demand), COD (chemical oxygen demand) and solids (suspended+dissolved) in POME are 4-17 g/L, 10-44 g/L, 20-100 g/L and 10-80 g/L respectively. On an elemental basis, of particular importance are carbon (about 25 g/L), potassium (2.3 g/L), nitrogen (0.8-1.4 g/L) and phosphorous (0.8 g/L). Several transition metals, such as iron, manganese, copper and zinc are found in POME at milligrams/L levels.
POME represents major oil yield losses. Oil droplets in POME consist of more than 80% neutral lipids, out of which >80% are triglycerides and most of the rest are diglycerides and 8.0% free fatty acids.
Due to its high BOD content, POME cannot be discharged to the environment as such and is biologically treated. Typically, processing of POME consists of employing a train of anaerobic, aerobic and/or facultative (anaerobic and aerobic) processes. The end products of anaerobic processing are mainly biogas (a mixture of methane 60-70% and CO2, 30-40%) and bio-solids and the end products of aerobic processing are essentially CO2 and bio-solids. The three most common treatment systems used are ponding systems, open tank digesters with extended aeration and closed tank digesters with biogas recovery and land applications. Hydraulic retention times in anaerobic and facultative ponding systems in open tank digesters or closed tank digesters are in the range of 20-45 and 16-20 days, respectively, which requires the use of large treatment systems, whose operation presents major difficulties. For example, in ponding systems, mixing is achieved by biogas bubbling which is inadequate for complete mixing, and leads to development of dead spots and short-circuiting in the ponds and therefore low efficiency. Oil delivered to anaerobic ponds tends to agglomerate and the rising solids brought to the surface by the biogas forms a sticky scum that is difficult to remove. Solids tend to build up in the ponds and regular de-sludging of the ponds is required. There is an urgent need to improve such systems and to minimize the environmental problems associated therewith.
The lignocellulosic coproducts of palm oil production are rich in polysaccharides (mainly cellulose and hemi-cellulose). Hydrolyzing such polysaccharides generates fermentable sugars. Many chemical and biological methods have been developed for the hydrolysis of the polysaccharides and subsequent fermentation of such fermentable sugars to form various fermentation products, mainly ethanol. Methods for the conversion of lignocellulosic material to fermentables other than sugars are known, as well.
Gutiérrez et. al. (“Process integration possibilities for biodiesel production from palm oil using ethanol obtained from lignocellulosic residues of oil palm industry” Bioresource Technology 100 (2009) 1227-1237) describe a process, whereby palm oil is produced from Fresh Fruit Bunches by commercial methods, sugars from lignocellulosic coproducts are fermented to ethanol, which is concentrated by distillation and dried on molecular sieves and then reacted with the palm oil in an extractive trans-esterification process to form ethyl esters of fatty acids, referred to as biodiesel, and glycerol. The following integration options were described in Gutiérrez:                Simultaneous saccharification and co-fermentation (SSCF): formation of hexoses and pentoses and simultaneous fermentation of the same        Consolidated bioprocessing (CBP): one microbial community is employed both for the production of cellulose hydrolytic enzymes and fermentation.        Reaction-separation integration in the multi-stage reactor-extractor for the trans-esterification.        Recirculation of material streams in order to achieve a better utilization of sugars, e.g. by implementing the recycling of water streams. The bottoms of ethanol rectification column and a fraction of the thin stillage are recycled back to the washing step of lignocellulosic biomass leaving the dilute acid pretreatment reactor. Thus, non-consumed pentoses and hexoses return to the SSCF reactor to be converted into ethanol.        The secondary steam from evaporators is condensed and recycled back to the pretreatment reactor where it is used as process water.        Recirculation of the distillate from the distillation column used for glycerol separation. This stream is fed to the rectification column in the ethanol production line.        The rectification column is also fed with the regenerate resulting from the adsorption in the molecular sieves.        Energy integration between both production lines: The heat released during the condensation of overhead vapors exiting the concentration and rectification columns is employed to provide the energy required by the flash unit processing the glycerol-enriched stream that leaves the reactor-extractor.        The purification of the two streams exiting the multi-stage reactor-extractor undergoes distillation using two columns and forming two ethanol-enriched streams. Those streams are recycled back to the reactor-extractor.        Energy integration by using the available heat of the condensers of both concentration and rectification columns in the ethanol production line for the distillation column employed for glycerol purification.        
While the integration processes suggested by Gutiérrez et. al., save on energy costs, they do not address some of the major problems of the palm oil industry, including yield losses, major environmental issues and poor economics. Gutiérrez et. al also produce a limited repertoire of products from the integrated processes he describes.